1. Field of the Invention
The invention relates to a pressure boosting system for at least one fuel injector of an internal combustion engine, having a hydraulic pressure booster.
2. Description of the Prior Art
A fuel injection system with pressure boosting, in which one central hydraulic pressure booster is provided for all the fuel injectors, is known from European Patent Disclosure EP 1 125 046 B1. The fuel supplied by means of a high-pressure pump is delivered to a central pressure reservoir (first common rail). The central pressure booster is downstream of the central pressure reservoir in the direction in which the fuel is supplied and carries the pressure-boosted fuel to a further pressure reservoir (second common rail), from which a plurality of pressure lines, corresponding in number to the number of injectors, leads away to the individual fuel injectors. The central pressure booster described in EP 1 125 046 B1, but also the other pressure boosters known, integrated with fuel injectors (as in German Patent Disclosure DE 103 25620 A1), have a pressure booster piston, which has a first piston portion with a first pressure booster piston part having a larger diameter and a second piston portion with a second pressure booster piston part having a small diameter D22. The one pressure booster piston part acts upon a high-pressure chamber for pressure boosting, and the other pressure booster piston part acts upon a control chamber or differential pressure chamber that is triggerable by an on-off valve. The pressure booster piston is guided axially movably inside a base body. A pressure face, which is exposed to a work chamber that acts as a hydraulic reservoir chamber and is subjected to the system pressure of the first common rail, is associated with the pressure booster piston on the pressure booster piston part having the larger diameter, on the diametrically opposed face end.
A disadvantage of the known pressure boosting system is the relatively large control quantity for triggering the pressure booster. If for multiple injections of small injection quantities, a boosted injection pressure is required, then the control chamber or differential pressure chamber of the pressure booster must be relieved upon each injection. The result is a large control quantity to be diverted, which must accordingly be included in the lost quantity in the injection system. Multiple injections within the context of a cylinder stroke motion are possible chronologically only within a narrowly defined window as well, since with each triggering of the pressure booster, its differential pressure chamber must refill with fuel. Moreover, with increasing injection pressures, the lost quantity increases proportionally to the fourth power by way of the gap width in the guide of the pressure booster piston, which adversely affects the hydraulic efficiency of such fuel injection systems.